Hybrid cement set-on-command compositions and methods of use

ABSTRACT

A method for isolating a portion of a wellbore including preparing a sealant composition includes an emulsion of an internal phase and an external phase. The sealant composition is placed into the wellbore where one phase sets upon subjecting the sealant composition to a thermal source followed by the setting of the other phase.

FIELD OF THE INVENTION

The present invention generally relates to cement compositions and moreparticularly to compositions and methods that allow for greater controlover the setting of fluids or slurries used in hydrocarbon explorationand production operations, such as subterranean cementing operations.

BACKGROUND OF THE INVENTION

Natural resources such as oil and gas located in a subterraneanformation can be recovered by drilling a wellbore down to thesubterranean formation, typically while circulating a drilling fluid inthe wellbore. After the wellbore is drilled, a string of pipe, e.g.,casing, can be run in the wellbore. The drilling fluid is then usuallycirculated downwardly through the interior of the pipe and upwardlythrough the annulus between the exterior of the pipe and the walls ofthe wellbore, although other methodologies are known in the art.

Cement is a unique material, which via a chemical reaction with water,transforms into a product having exceptional mechanical properties. Inusual applications, cement slurry is formed by mixing cement and water,which results in a chemical reaction. In an early stage of the reaction,the cement slurry can be shaped into a required shape. The shapingproperty of the cement slurry allows for the use of cement in a widerange of industrial applications, including civil engineering and theoil and gas industry.

Hydraulic cement compositions are commonly employed in the drilling,completion and repair of oil and gas wells. For example, hydrauliccement compositions are utilized in primary cementing operations wherebystrings of pipe such as casing or liners are cemented into wellbores. Inperforming primary cementing, a hydraulic cement composition is pumpedinto the annular space between the walls of a wellbore and the exteriorsurfaces of a pipe string disposed therein. The cement composition isallowed to set in the annular space, thus forming an annular sheath ofhardened substantially impermeable cement. This cement sheath physicallysupports and positions the pipe string relative to the walls of thewellbore and bonds the exterior surfaces of the pipe string to the wallsof the wellbore. The cement sheath prevents the unwanted migration offluids between zones or formations penetrated by the wellbore. Hydrauliccement compositions are also commonly used to plug lost circulation andother undesirable fluid inflow and outflow zones in wells, to plugcracks and holes in pipe strings cemented therein and to accomplishother required remedial well operations. After the cement is placedwithin the wellbore a period of time is needed for the cement to cureand obtain enough mechanical strength for drilling operations to resume.This down time is often referred to as “waiting-on-cement”, or WOC. Ifoperations are resumed prior to the cement obtaining sufficientmechanical strength, the structural integrity of the cement can becompromised.

Two common pumping methods have been used to place the cementcomposition in the annulus. The cement composition may be pumped downthe inner diameter of the casing and up through the annulus to itsdesired location. This is referred to as a conventional-circulationdirection method. Alternately, the cement composition may be pumpeddirectly down the annulus so as to displace well fluids present in theannulus by pushing them up into the inner diameter of the casing. Thisis referred to as a reverse-circulation direction method. Cement canalso be used within the wellbore in other ways, such as by placingcement within the wellbore at a desired location and lowering a casingstring into the cement. The latter method may be used, for example, whenthere is not the ability to circulate well fluids due to fluid loss intoa formation penetrated by the wellbore.

In carrying out primary cementing as well as remedial cementingoperations in wellbores, the cement compositions are often subjected tohigh temperatures, particularly when the cementing is carried out indeep subterranean zones. These high temperatures can shorten thethickening times of the cement compositions, meaning the setting of thecement takes place before the cement is adequately pumped into theannular space. Therefore, the use of set retarding additives in thecement compositions has been required. These additives extend thesetting times of the compositions so that adequate pumping time isprovided in which to place the cement into the desired location.

While a variety of cement set retarding additives have been developedand utilized, known additives, such as sugars or sugar acids, canproduce unpredictable results. Hydroxy carboxylic acids, such astartaric acid, gluconic acid and glucoheptonic acid are commonly used inoil well cementing as a cement retarder. However, if an excess ofhydroxy carboxylic acid, or any other retarder, is used it canover-retard the set of the cement slurry and thereby causing it toremain fluid for an extended period of time. This over-retardation canresult in extended waiting time prior to resuming drilling and may allowgas to invade the slurry thereby causing unwanted gas migration. Theextended waiting time results in delays in subsequent drilling orcompletion activities.

In a number of cementing applications, aqueous salt has been utilized asan additive in cement compositions. The salt, generally sodium chloride,functions as a dispersant in cement slurry, causing the slurry to expandupon setting whereby the attainment of a good bond between the wellboreand casing upon setting of the slurry is enhanced. However, saltsaturated slurries can cause problems to bordering formations, and incertain situations salt can be leached out of the cement slurry, whichcould cause cement failure. Also, certain salts, such as calcium salts,can act as accelerating agents if added in sufficient amounts, which canreduce the setting time of the cement composition. However, the presenceof a set and strength accelerating agent, such as calcium salt, in thecement composition increases the risk that the cement composition maythicken or set before placement. Given the complexity of the cementchemistry and the large temperature and pressure gradients that can bepresent in the wellbore, and the difficulty in predicting the exactdownhole temperatures during the placement and setting of the cement, itcan be difficult to control the retarding additive and acceleratingagent to get the desired setting behavior. Systems generally areover-engineered to have very long setting (or thickening) times in orderto ensure that the mix remains fluid until all of the cementitiousmaterial is in place which can result in excessive WOC.

Therefore, there is a need for a new cement containing material as wellas improved set control methods, which bring about predictable cementcomposition setting times in the subterranean environments encounteredin wells in addition to lowered WOC. In particular, it is desirable todevelop methods for rapidly setting cement-based systems whereby thetiming of the setting is under the control of technicians in the fieldwithout the risk of premature setting. Thus, a need exists for a methodof cementing a wellbore that would simultaneously contain sufficientretarder material to ensure proper pumpability for the desired pumpingduration and a sufficient concentration of an accelerator to shorten thesetting time, whereby the thickening effect of the accelerator is underthe control of technicians in the field.

SUMMARY OF THE INVENTION

The present invention generally relates to wellbore fluid and/or slurrycompositions that allow for greater control over the setting of suchcompositions in a wellbore.

Disclosed herein is a sealant composition in the form of an emulsioncontaining an organic phase and an aqueous phase. The sealantcomposition can include one or more components selected from sealants,resins, cements, settable drilling muds, conformance fluids, andcombinations thereof. The aqueous phase can include a cement slurrycontaining cement and water. The cement slurry may also contain a setmodifier. The set modifier can include one or more components selectedfrom an accelerator, an oxidizing agent, a set retarder or combinationsthereof. The organic phase can be a polymerizable organic continuousphase, or monomer phase, which is capable of being polymerized into arigid material. The resulting polymer is a porous structure that acts asa scaffold for the cement slurry, holding the cement slurry in placeuntil the cement slurry eventually sets. After the final setting of thecement, the resulting composition may include two interpenetratingnetworks: a network of a porous polymer structure containing a networkof set cement. After setting, the resulting composition may includemultiple non-continuous networks of set cement. In an aspect, theresulting composition may include a continuous network of set cement.Alternately the organic phase can be a thermo-setting resin that iscapable of setting into a rigid material.

The organic phase can include non-water soluble liquid monomers,functionalized polymers, oligomers, resins or combinations thereof. Themonomer component can include vinyl monomers. In an aspect the monomercan include, but is not limited to: methyl acrylate, ethyl acrylate,butyl acrylate, methylstyrene, styrene, methyl methacrylate orcombinations thereof. The monomers may be polymerizable upon theaddition of an initiator, upon being subjected to sufficient thermalenergy. The organic phase may also include one or more selected from acrosslinking agent, a surfactant, a stabilizer, an initiator andcombinations thereof.

Also disclosed herein is a method of isolating a portion of a wellboreby preparing a sealant composition, optionally in the form of anemulsion, containing an organic phase and an aqueous phase. The sealantcomposition is placed into a wellbore and allowed to set in thewellbore. The setting of the sealant composition in the wellbore can beaccomplished in two stages, wherein the organic phase is set firstfollowed by the setting of the aqueous phase. The organic phase mayinclude one or more selected from a crosslinker, a surfactant, astabilizer, an initiator and combinations thereof.

The stage of setting the organic phase can include the polymerization ofthe organic phase. The polymerization of the organic phase can beinitiated by adding a polymerization initiator to the organic phase andby subjecting the organic phase to thermal energy. Alternately thesetting of the organic phase can include the setting of a thermo-settingresin with the input of thermal energy.

In an embodiment the polymerization of the organic phase can beinitiated by the addition of an initiator. The initiator can be selectedto initiate the polymerization of the organic phase at a temperature ofat least a portion of the wellbore, such as at a portion having anelevated temperature, for example the portion of the wellbore that hasthe highest temperature. The initiator can be chosen based on thewellhead temperature. The initiator may also be selected having a higherdecomposition temperature than the temperature in the wellhead to avoidpremature polymerization. In an aspect the initiator may be selectedfrom the group consisting of, but not limited to: azo-initiators such as2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile),2,2′-azobis(2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile,dimethyl 2,2′-azobisisobutyrate, 2,2′-azobis(2-methylbutyronitrile),1,1′-azobis(1-cyclohexanecarbonitrile),2-(carbamoylazo)isobutyronitrile, 2,2′-azobis(2,4,4-trimethylpentane),2-phenylazo-2,4-dimethyl-4-methoxyvaleronitrile, and2,2′-azobis(2-methylpropane) and combinations thereof. Other initiatorscan include peroxy-initiators such as persulfates, benzoyl peroxide,tert-butyl peroxide, and combinations thereof.

The polymerization of the organic phase can be initiated by subjectingthe organic phase to thermal energy. In an embodiment the thermal energyis supplied by an outside source, such as a heating element, which maybe under the control of employees in the field. In another embodiment,the thermal energy is supplied by naturally occurring thermal energypresent in the wellbore.

The aqueous phase of the method of the current invention includeshydraulic cement and sufficient water to form a slurry. The method canalso include the step of adding additives to the slurry prior to placingthe slurry into a wellbore. The additives can include an accelerator, aset retarder or combinations thereof.

The preceding has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention may be more fully understood. The featuresand technical advantages of the present invention will be readilyapparent to those skilled in the art upon a reading of the detaileddescription of the embodiments of the invention, which follows.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a cross sectional side view of a wellbore.

FIG. 2 compares the setting times of four cement mixtures at a constanttemperature.

FIG. 3 represents a stress/strain curve of a neat cement sample.

FIG. 4 represents a stress/strain curve of a HIPE cement sample.

FIG. 5 represents a stress/strain curve of a neat cement sample withBorax.

FIG. 6 represents a stress/strain curve of a HIPE cement sample withBorax.

DETAILED DESCRIPTION

The present invention relates generally to wellbore operations involvingfluids or slurries, and more particularly, to fluids or slurries thatcontain accelerating agents and/or retarders that can be released,activated and/or deactivated on command to provide thickening to thefluid or slurry. The fluids or slurries referred to herein can be anysuitable for wellbore operations, drilling, completion, workover orproduction operations such as cements, drilling muds, lost circulationfluids, fracturing fluids, conformance fluids, sealants, resins, etc.One embodiment of the present invention relates to wellbore cementingoperations, and more particularly, to methods of cementing in wellboresusing sealant compositions having two phases.

The sealant compositions disclosed herein generally contain an organicphase including a monomer component and an aqueous phase including waterand a cement component such as hydraulic cement, which can includecalcium, aluminum, silicon, oxygen, and/or sulfur that sets and hardensby reaction with the water.

Referring to FIG. 1, a cross sectional side view of an embodiment of awellbore 2 is illustrated. Surface casing 4, having a wellhead 6attached, is installed in the wellbore 2. Casing 8 is suspended from thewellhead 6 to the bottom of the wellbore 2. An annulus 10 is definedbetween casing 8 and the wellbore 2. Annulus flow line 12 fluidlycommunicates with annulus 10 through the wellhead 6 and/or surfacingcasing 4 with an annulus valve 14. Flow line 16 is connected to thewellhead 6 to allow fluid communication with the inner diameter ofcasing 8 and a casing valve 18. At the lower most end of casing 8 thecasing is open to the wellbore 2 or has circulation ports in the wallsof casing 8 (not shown) to allow fluid communication between the annulus10 and the inner diameter of casing 8.

A sealant composition can be pumped down the casing 8 and circulated upthe annulus 10 while fluid returns are taken from the annulus 10 outflow line 12, in a typical circulation direction. Alternately thesealant composition can be pumped into the annulus 10 from annulus flowline 12 while fluid returns are taken from the inner diameter of casing8 through flow line 16. Thus, fluid flows through wellbore 2 in areverse circulation direction.

In one method a fluid composition, such as a sealant composition, can beplaced within the wellbore 2 and a sealed or filled tubular, such ascasing 8, can be lowered into the wellbore 2 such that the fluidcomposition is displaced into the annulus 10 area, thereby placing thefluid composition within the annulus 10 without pumping the fluidcomposition into the annulus 10. The above method can be referred to aspuddle cementing. The fluid composition can be a drilling fluid placedwithin the wellbore after drilling operations are complete.

Any cement suitable for use in subterranean applications may be suitablefor use in the present invention. In certain embodiments, the sealantcompositions used in the present invention include hydraulic cement.Examples of hydraulic cements include but are not limited to Portlandcements (e.g., Classes A, C, G, and H Portland cements), pozzolanacements, gypsum cements, phosphate cements, high alumina contentcements, silica cements, high alkalinity cements, and combinationsthereof. Cements including shale, cement kiln dust or blast furnace slagalso may be suitable for use in the present invention. In certainembodiments, the shale may include vitrified shale; in certain otherembodiments, the shale may include raw shale (e.g., unfired shale), or amixture of raw shale and vitrified shale.

The sealant compositions used in the present invention generally includean aqueous-based base fluid and a nonaqueous-based base fluid. Theaqueous-based base fluid may include water that may be from any source,provided that the water does not contain an excess of compounds (e.g.,dissolved organics, such as tannins) that may adversely affect othercompounds in the cement compositions. For example, a cement compositionuseful with the present invention can include fresh water, salt water(e.g., water containing one or more salts dissolved therein), brine(e.g., saturated salt water), or seawater. The nonaqueous-based basefluid may include any number of organic liquids. Examples of suitableorganic liquids include, but are not limited to, mineral oils, syntheticoils, esters, and the like. The nonaqueous-based base fluid may includea monomer component. In an embodiment, the monomer component includes,but is not limited to, liquid monomers that are not water-soluble. In amore specific embodiment, the monomers are vinyl monomers having anaccessible polymerizable double bond. In an aspect the monomer can beselected from the group of methyl acrylate, ethyl acrylate, butylacrylate, methylstyrene, styrene and methyl methacrylate andcombinations thereof. The nonaqueous-based base fluid may include a lowviscosity thermo-setting resin.

The aqueous-based base fluid and the nonaqueous-based base fluid areimmiscible to each other when mixed, thus forming an aqueous internalphase and an organic external phase. The aqueous internal phase may bereferred to as the aqueous phase and the organic external phase may bereferred to as the organic phase and as an organic continuous phase. Theaqueous-based base fluid may be present in the cement slurry in anamount sufficient to form a pumpable slurry. More particularly, theaqueous-based base fluid may be present in the cement slurry used in thepresent invention in an amount in the range of from about 25% to about150% by weight of cement (“bwoc”). In certain embodiments theaqueous-based base fluid may be present in the cement slurry in therange of from about 30% to about 75% bwoc. In still other embodimentsthe aqueous-based base fluid may be present in the cement slurry in therange of from about 40% to about 60% bwoc. In still other embodimentsthe aqueous-based base fluid may be present in the cement slurry in therange of from about 35% to about 50% bwoc. The cement slurry may includea sufficient amount of water to form a pumpable cementitious slurry. Thewater may be fresh water or salt water, e.g., an unsaturated aqueoussalt solution or a saturated aqueous salt solution such as brine orseawater.

As a non-limiting example the aqueous phase can include a lowconcentration salt electrolyte solution in an amount of about 0.5% toabout 20% by volume of the aqueous phase and a cement slurry in anamount of about 75% to about 95% by volume of the aqueous phase. Theaqueous phase can also include a set modifier. The set modifier caninclude an accelerator in an amount of from about 0.1% to about 20% byweight of the aqueous phase. The set modifier can also include anoxidizing agent in an amount of about 0.05% to about 5% by weight of theaqueous phase capable of attacking any set retarder present. The setmodifier can include a set retarder in an amount from about 0.1% toabout 10% by weight of the aqueous phase.

The sealant composition may be in the form of an emulsion containing anexternal phase and an internal phase. The external phase is the organicphase and the internal phase is the aqueous phase. In an aspect theinternal phase is present in the emulsion in amounts of from about 50%to about 90% of the total volume of the emulsion. Alternatively, theinternal phase is present in the emulsion in amounts of from about 60%to about 80% of the total volume of the emulsion. In an embodiment, theexternal phase is present in the emulsion in amounts of from about 10%to about 50% of the total volume of the emulsion. Alternatively, theexternal phase is present in the emulsion in amounts of from about 20%to about 40% of the total volume of the emulsion. In a more specificembodiment, the emulsion is a high internal phase emulsion. The highinternal phase emulsion contains greater than 74% of the total volume ofthe emulsion.

The emulsion, containing an internal phase and an external phase, mayhave a certain volumetric ratio of internal phase to external phase. Inan aspect the volumetric ratio of internal phase to external phase is offrom 9:1 to 1:1. In another aspect the volumetric ratio of internalphase to external phase is of from 7:1 to 1:1. Alternatively, thevolumetric ratio of internal phase to external phase is of from 5:1 to1:1. Alternatively, the volumetric ratio of internal phase to externalphase is of from 4:1 to 1.5:1.

Optionally, the aqueous phase fluid or slurry compositions used in thepresent invention may include a fluid loss control additive. A varietyof fluid loss control additives may be suitable for use with the presentinvention, including, inter alia, fibers, flakes, particulates, modifiedguars, latexes, and 2-acrylamido-2-methylpropanesulfonic acid copolymerssuch as those that are further described in U.S. Pat. Nos. 4,015,991;4,515,635; 4,555,269; 4,676,317; 4,703,801; 5,339,903; and 6,268,406,the entire disclosures of which are hereby incorporated herein byreference. Generally, the fluid loss control additive is present in thecement slurry used in the present invention in an amount sufficient toprovide a desired degree of fluid loss control. More particularly, thefluid loss control additive may be present in the cement slurry used inthe present invention in an amount in the range of from about 0.1% toabout 10% bwoc. In certain embodiments, the fluid loss control additiveis present in the cement slurry used in the present invention in anamount in the range of from about 0.2% to about 3% bwoc.

Optionally, the compositions used in the present invention also mayinclude a mechanical-property modifier. Examples of suitablemechanical-property modifiers may include, inter alia, gases that areadded at the surface (e.g., nitrogen), gas-generating additives that maygenerate a gas in situ at a desired time (e.g., aluminum powder orazodicarbonamide), hollow microspheres, elastomers (e.g., elasticparticles including a styrene/divinylbenzene copolymer), high aspectratio materials (including, inter alia, fibers), resilient graphiticmaterials, vapor/fluid-filled beads, matrix-sorbable materials havingtime-dependent sorption (initiated by, e.g., degradation), mixturesthereof (e.g., mixtures of microspheres and gases), or the like. Incertain embodiments of the present invention, the optionalmechanical-property modifier may include a latex.

In certain optional embodiments wherein microspheres are added to afluid or slurry, such as cement compositions useful with the presentinvention, the microspheres may be present in the cement compositions inan amount in the range of from about 5% to about 75% bwoc. In certainembodiments of the present invention, the inclusion of microspheres inthe cement compositions useful with the present invention may reduce thedensity of the cement composition.

In certain optional embodiments wherein one or more gas-generatingadditives are used as mechanical property modifiers in the aqueous phasefluid or slurry compositions used in the present invention, the one ormore gas-generating additives may include, inter alia, aluminum powderthat may generate hydrogen gas in situ, or they may includeazodicarbonamide that may generate nitrogen gas in situ. Certaininitiators can also generate gases in situ such as azo-initiators andperoxides. Other gases and/or gas-generating additives also may besuitable for inclusion in the fluid or slurry compositions used in thepresent invention. Where included, a gas-generating additive may bepresent in aqueous phase cement compositions in an amount in the rangeof from about 0.1% to about 5% bwoc. In certain embodiments where thegas-generating additive is aluminum powder, the aluminum powder may bepresent in the aqueous phase cement compositions in an amount in therange of from about 0.1% to about 1% bwoc. In certain embodiments wherethe gas-generating additive is an azodicarbonamide, the azodicarbonamidemay be present in the aqueous phase cement compositions in an amount inthe range of from about 0.5% to about 5% bwoc.

Optionally, the aqueous phase fluid or slurry compositions used in thepresent invention also may include additional suitable additives,including defoaming agents, dispersants, density-reducing additives,surfactants, weighting materials, viscosifiers, fly ash, silica, freewater control agents, and the like. Any suitable additive may beincorporated within the aqueous phase fluid or slurry compositions usedin the present invention.

The aqueous phase fluid or slurry compositions used in the presentinvention can further include a set retarder. Set retarding admixtureslengthen the time at which the fluid or slurry composition remains afluid. These retarding admixtures consequently allow a fluid or slurry,such as cement, to be pumped along long distances without the effect ofpremature setting. A broad variety of set retarders may be suitable foruse in the fluid or slurry compositions used in the present invention.For example, the set retarder may include, inter alia, phosphonic acid,phosphonic acid derivatives, lignosulfonates, salts, sugars,carbohydrate compounds, organic acids, carboxymethylatedhydroxyethylated celluloses, synthetic co- or ter-polymers includingsulfonate and carboxylic acid groups, and/or borate compounds. Incertain embodiments, the set retarders used in the present invention arephosphonic acid derivatives, such as those described in U.S. Pat. No.4,676,832, the entire disclosure of which is hereby incorporated herein.Examples of suitable borate compounds include, but are not limited to,sodium tetraborate and potassium pentaborate. Examples of suitableorganic acids include, inter alia, gluconic acid and tartaric acid.Generally, the set retarder is present in the aqueous phase fluid orslurry compositions used in the present invention in an amountsufficient to delay the setting of the fluid or slurry composition in asubterranean formation for a desired time. More particularly, the setretarder may be present in the aqueous phase fluid or slurrycompositions used in the present invention in an amount in the range offrom about 0.1% to about 10% bwoc. In certain embodiments, the setretarder is present in the aqueous phase fluid or slurry compositionsused in the present invention in an amount in the range of from about0.5% to about 4% bwoc.

The slurry compositions of the present invention may also include anaccelerator. The accelerator aids in overcoming possible delays causedby the set retarders by shortening the setting time of the fluid orslurry composition. A broad variety of accelerators may be suitable foruse in the fluid or slurry compositions used in the present invention,the accelerator may include any component that reduces the setting timeof a cement composition. For example, the accelerator may include alkaliand alkaline earth metal salts, silicate salts, aluminates and amines,such as triethanolamine. In an embodiment, the accelerator can include acalcium salt, a sodium salt, or combinations thereof. The calcium saltmay be selected from the group consisting of calcium formate, calciumnitrate, calcium nitrite and calcium chloride. The sodium salt caninclude sodium sulfate. In a specific embodiment, the accelerator iscalcium chloride. The accelerator may be present in the fluid or slurrycompositions used in the present invention in an amount in the range offrom about 0.1% to about 20% bwoc. In certain embodiments, theaccelerator is present in the cement slurry used in the presentinvention in an amount in the range of from about 4% to about 12% bwoc.The nonaqueous-based base fluid, or organic phase, of the invention mayinclude but is not limited to a monomer component. In an embodiment, themonomer component includes liquid monomers that are not water-soluble.In a more specific embodiment, the monomers are vinyl monomers having anaccessible polymerizable double bond. In an aspect the monomer can beselected from the group of methyl acrylate, ethyl acrylate, butylacrylate, methylstyrene, styrene and methyl methacrylate andcombinations thereof.

In an embodiment the nonaqueous-based base fluid, or organic phase, ofthe invention may include but is not limited to a low viscositythermo-setting resin. The resin can be immiscible in water and can anepoxy type sealing composition that can harden such as those disclosedin U.S. Pat. Nos. 5,875,844; 5,875,845; and 6,068,055 to Chatterji etal. which are incorporated herein by reference. One non-limiting exampleof a low viscosity thermo-setting resin is available from Halliburtonunder the brand name Strata-Loc®.

The organic phase may also include but is not limited to a crosslinker,a surfactant, or an initiator, or combinations thereof. Crosslinkingagents, or crosslinkers, are well known in the art and may include butare not limited to monomers having two or more polymerizable doublebonds, such as divinylbenzene. The crosslinking agent may bond duringpolymerization and connect distinct monomers, thereby forming acrosslink between two monomer chains. Surfactants may include but arenot limited to those suitable for forming w/o (water-in-oil) emulsions,such as Hypermer™ polymeric surfactants. Initiators may include but arenot limited to azo-initiators such as2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile),2,2′-azobis(2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile,dimethyl 2,2′-azobisisobutyrate, 2,2′-azobis(2-methylbutyronitrile),1,1′-azobis(1-cyclohexanecarbonitrile),2-(carbamoylazo)isobutyronitrile, 2,2′-azobis(2,4,4-trimethylpentane),2-phenylazo-2,4-dimethyl-4-methoxyvaleronitrile, or2,2′-azobis(2-methylpropane) or combinations thereof. Other initiatorscan include peroxy-initiators such as persulfates, benzoyl peroxide,tert-butyl peroxide, and combinations thereof.

Referring to FIG. 2, a graph is depicted in FIG. 2 indicating thesetting times of four samples. The setting times of each sample wereconducted at the same temperature. The four samples include a neatcement mixture not containing the organic phase (Neat Class A), a cementmixture not containing an organic phase but containing a retarder (ClassA+Borax), a cement mixture containing an organic phase (HIPE (highinternal phase emulsion)), and a cement mixture containing an organicphase and a retarder (HIPE+Borax). In both samples not containing anorganic phase, Neat Class A and Class A+Borax, once the setting isinitiated, it continues until the composition is fully set. In bothcases in which the samples contain an organic phase, HIPE andHIPE+Borax, a brief setting period occurs, in this case for about 1 to 2hours, followed by a pause in the setting for about 5 hours, followed bythe resumption of setting until the mixture is fully set. In addition,in both HIPE cases, the initial setting resulted in a 15-30% reductionin transit time (μsec/in.), with the remaining reduction in transit timeoccurring in the second setting (when the setting resumes). This firstsetting is a result of the polymerization of the monomer component ofthe organic phase. The polymerized organic phase acts as a scaffold orlattice that supports the cement slurry until the cement slurry finallysets. The scaffold structure can enable the continuation of drillingactivities while the cement slurry is still setting. In addition, sincethe sealant composition is not fully set, errors can be corrected oralterations to a cementing procedure may be made prior to the fullsetting of the cement.

FIGS. 3 and 4 illustrate a stress/strain curve of two cement samples.FIG. 3 illustrates a stress/strain curve of a neat cement sample. Thestress/strain curve of FIG. 3 indicates that a neat cement compositionhas a breaking point at a stress of about 5500 psi and a breaking pointat a strain of 0.03 inches. FIG. 4 illustrates a stress/strain curve ofa HIPE cement sample. The stress/strain curve of FIG. 4 indicates that aHIPE cement composition has a breaking point at a stress of about 4000psi and a breaking point at a strain of 0.045 inches. These figuresindicate that the HIPE cement has a greater strain resistance and thus ahigher resiliency to impact. Cement having a higher resiliency allowsfor greater protection of the casing/cement/wellbore bonding duringworking conditions.

Methods of this invention for isolating a portion of a wellbore mayinclude forming a sealant composition having two phases and pumping thesealant composition into a wellbore. The two phases can include anaqueous phase and an organic phase, which are immiscible to each other.The aqueous phase and the organic phase may be prepared separately andlater combined to form an emulsion. The sealant composition is placedinto a wellbore and allowed to set into the wellbore. The setting of thesealant composition into the wellbore can be accomplished in two stages,wherein the organic phase is set first followed by the setting of theaqueous phase.

The stage of setting the organic phase can include the polymerizing ofthe organic phase. The polymerization of the organic phase can beinitiated by adding a polymerization initiator to the organic phase, bysubjecting the organic phase to thermal energy. The stage of setting theorganic phase can be the first stage of the setting process. The setorganic phase provides a polymeric component, which can act as ascaffold to support the unset cement slurry.

In an embodiment the polymerization of the organic phase can beinitiated by the addition of an initiator. In a further embodiment theinitiator is sufficient to initiate the polymerization of the organicphase. The initiator can be chosen based on the wellhead temperature.The initiator can be selected to initiate the polymerization of theorganic phase at a temperature of at least a portion of the wellbore. Inan embodiment, the initiator can be selected to initiate thepolymerization of the organic phase at a temperature of at least aportion of the bottom half of the length of the wellbore. In anotherembodiment, the initiator can be selected to initiate the polymerizationof the organic phase at a temperature of at least a portion of the tophalf of the length of the wellbore. The initiator may also be selectedhaving a higher decomposition temperature than the temperature in thewellhead to avoid premature polymerization.

The polymerization of the organic phase can be initiated by subjectingthe organic phase to thermal energy. In an embodiment the thermal energyis supplied by an outside source, such as a heating element, which maybe under the control of employees in the field. The heating element maycomprise high strength carbon fibers, which may be submerged into theemulsion that is placed into the wellbore. The thermal energy can besupplied by any suitable source, such as in the non-limiting examples ofhydraulic forces; exothermic chemical reactions; and induction,resistance, and other electrical current methods that can generate heat.In another embodiment, the thermal energy is supplied by naturallyoccurring thermal energy present in the wellbore.

In an embodiment, the thermal energy is introduced under the control ofa technician in the field. The technician, engineer, or other on-siteemployee, can have the control over the emission of thermal energy bysending a signal that causes a release of thermal energy from anemitter. In this embodiment, the thermal energy is released on demandfrom the technician in the field. The thermal energy can be released bya control system having parameters such as timer, flow meter,temperature sensor, or the like. In another embodiment, the loweringand/or emitting of the thermal energy source is triggered by a timingmechanism. In a further embodiment, the lowering and/or emitting of thethermal energy source is triggered by a flow meter that detects theamount of the intermixed composition delivered into the wellbore.

The aqueous phase of the method of the current invention includeshydraulic cement and sufficient water to form a slurry. The method canalso include the step of adding an accelerator to the slurry, placingthe slurry containing the accelerator into a wellbore. The acceleratorcan include a calcium salt, a sodium salt, or combinations thereof. Inan embodiment, the accelerator can include CaCl₂ or Na₂SO₄ orcombinations thereof. The accelerator can be added in an amount of fromabout 0.01% to about 20% by weight of cement. In another embodiment, theaccelerator can be added in an amount of from about 0.2% to about 1% byweight of cement. The method can also include the step of adding a setretarder to the slurry before placing the slurry into a wellbore.

A medium phase (an emulsion containing an internal phase volume of 30-74vol. %) to high phase (an emulsion containing an internal phase volumemore than 74 vol. %) emulsion containing a liquid cement slurry may beformed by the drop-wise addition of an electrolyte solution, containingwater and CaCl₂ or Na₂SO₄ or combinations thereof, but not limited bythese examples, into the organic phase, followed by the fast addition ofa cement slurry while the mixture is constantly stirred at a low firstspeed. The emulsion mixture is then stirred at a faster second speed.The first speed may range between about 100 to 700 rpm. The second speedmay range between about 1000 to 2000 rpm.

Methods of this invention for isolating a wellbore may include forming asealant composition that includes an emulsion of an aqueous phase thatincludes hydraulic cement and an organic phase that includes a monomercapable of polymerization, and including a set modifier, pumping thesealant composition containing the set modifier into a wellbore andsubjecting the sealant composition to thermal energy after placementinto the wellbore. The set modifier of the invention may be a retarder.The retarder of the invention can be susceptible to thermal energy orhave a threshold temperature. The thermal energy introduced issufficient to dissolve, or otherwise break down, the retarder thusallowing the setting of the sealant composition to proceed.

Alternate methods of this invention for isolating a wellbore may includeforming a sealant composition that includes an emulsion of an aqueousphase that includes hydraulic cement and an organic phase that includesa low viscosity thermo-setting resin. The resin can be immiscible inwater and can a hardenable epoxy type sealing composition such as thosedisclosed in U.S. Pat. Nos. 5,875,844; 5,875,845; and 6,068,055 toChatterji et al. which are each incorporated herein by reference intheir entirety. One non-limiting example of a low viscositythermo-setting resin is available from Halliburton under the brand nameStrata Loc®.

EXAMPLES Example 1

High internal phase emulsions (emulsions having an internal phase volumeof 80%) were prepared in a glass reaction vessel equipped with a glasspaddle rod connected to an overhead stirrer. The organic continuousphase of the emulsion contained 80 vol. % monomers (50:50 by volumemonomer (styrene):crosslinker (divinylbenzene)), 20 vol. % of thesurfactant (Hypermer™ 2296), and 1 mol % initiator(azobisisobutyronitrile, AIBN) with respect to the monomers. Theinitiator was first dissolved in half of the amount of monomer and thenadded to the rest of the organic phase. The addition of the internalphase was carried out in two steps: first, an aqueous solutioncontaining 0.5 wt. % CaCl₂ was added dropwise into the organic phasewhile the mixture was stirred at a stirring rate of 400 rpm. The aqueoussolution contained 14% of the total volume of the internal phase.Secondly, the cement slurry comprising the remaining 86% of the totalvolume of the internal phase was added slowly. The cement itself wasprepared by adding dry cement and retarder (Borax) (in an amount of 0.3wt. % of the cement weight) into water and homogenizing the mixture withan electric mixer for 35 seconds (the mixture had a cement/water ratioof 1/0.38 (aqueous phase contained only water)). After the entireinternal phase was added into the organic phase, the stirring rate wasincreased to 1500 rpm for final homogenization.

For conventional polymerization, the prepared high internal phaseemulsion cement hybrid (HIPECH) was transferred into plastic tubes,sealed and placed into an oven for 24 hours (although the polymerizationwas complete after 3-4 hours) at 70° C. for polymerization of theorganic phase. For express polymerization, the prepared high internalphase emulsion cement hybrid (HIPECH) was transferred into a glassvessel. Carbon fibers (Toray™ M40B, 12000-50B), which were eithersubmerged into the liquid HIPECH or wrapped around the glass vessel orsteel pipe were used as resistance heaters to initiate the expresspolymerization process. Approximately 10-12 W (Watts) were used topolymerize a HIPECH volume of 30 cm³. The polymerization, i.e. settingof the organic phase of the HIPECH, was complete after 80-90 min. Theproperties of the polyHIPECH (polymerized HIPECH) obtained using expresspolymerization were compared with samples obtained using conventionalthermal polymerization process.

Example 2

Medium internal phase emulsions (emulsions having an internal phasevolume of 70 vol. %) were prepared in a glass reaction vessel equippedwith a glass paddle rod connected to an overhead stirrer. The organiccontinuous phase of the emulsion contained 80 vol. % monomers (50:50 byvolume monomer (styrene):crosslinker (divinylbenzene)), 30 vol. % of thesurfactant (Hypermer 1031), and 1 mol % initiator(azobisisobutyronitrile, AIBN) with respect to the monomers. Theinitiator was first dissolved in half of the amount of monomer and addedto the rest of the organic phase. The addition of the internal phase wascarried out in two steps: first, an aqueous solution containing 0.5 wt.% CaCl₂ was added dropwise into the organic phase while the mixture wasstirred at a stirring rate of 400 rpm. The aqueous solution contains 14vol. % of the total volume of the internal phase. Secondly, the cementslurry comprising the remaining 86 vol. % of the total volume of theinternal phase was added slowly. The cement itself was prepared byadding dry cement and retarder (Borax) (in an amount of 0.3 wt. % of thecement weight) into water and homogenizing the mixture with an electricmixer for 35 seconds (the mixture had a cement/water ratio of 1/0.38(aqueous phase contained only water)). After the entire internal phasewas added into the organic phase, the stirring rate was increased to1500 rpm for final homogenization.

For conventional polymerization, the prepared high internal phaseemulsion cement hybrid (HIPECH) was transferred into plastic tubes,sealed and placed into an oven for 24 hours (although the polymerizationwas complete after 3-4 hours) at 70° C. for polymerization of theorganic phase. For express polymerization, the prepared high internalphase emulsion cement hybrid (HIPECH) was transferred into a glassvessel. Carbon fibers (Toray™ M40B, 12000-50B), which were eithersubmerged into the liquid HIPECH or wrapped around the glass vessel orsteel pipe were used as resistance heaters to initiate the expresspolymerization process. Approximately 10-12 W (Watts) were used topolymerize a HIPECH volume of 30 cm³. The polymerization, i.e. settingof the organic phase of the HIPECH, was complete after 80-90 min. Theproperties of the polyHIPECH (polymerized HIPECH) obtained using expresspolymerization were compared with samples obtained using conventionalthermal polymerization process.

Example 3

HIPE samples were prepared by obtaining a mixture of 24 ml of styrene,24 ml of divinylbenzene, 12 ml of Hypermer™ 1031, and 0.54 g ofazobisisobutyronitrile and adding to the mixture, by dropwise addition,20 ml of 0.5% calcium chloride solution under a sufficient shear toemulsify. Next, a cement slurry prepared from 320 g of Class A cementand 120 g of water was slowly added to the mixture. After all the cementslurry was added, the shear was increased to about 7000 rpm and themixture was blended for two minutes. The properties of the HIPE cementsamples were compared with samples of traditional cement.

A test comparison involved the ultrasonic cement analysis of 4 samples.The first sample included HIPE cement. The second sample included HIPEcement with the addition of a set retarder (Borax). The third sampleincluded neat cement and the fourth sample included neat cement with theaddition of a set retarder (Borax). The results of these tests areindicated in FIG. 2. The results are also indicated in the tables belowas follows:

TABLE 1 Ultrasonic Cement Analysis of HIPE Cement Rate of Change inElapsed Pressure Transit Time Transit Time Time (hrs) Temp (° F.) (psi)μsec/in. μsec/in/hr. 0.0 84 3133 18.1 — 1.0 165 3265 18.69 +0.59 2.0 1583506 16.49 −2.2 3.0 158 3141 16.32 −0.17 4.0 158 3197 16.2 −0.12 5.0 1583068 16.15 −0.05 6.0 158 3044 16.08 −0.07 7.0 158 3130 15.93 −0.15 8.0158 3162 15.22 −0.71 9.0 158 3008 13.64 −1.58 10.0 158 3253 12.73 −0.9111.0 158 3104 12.32 −0.41 12.0 158 3042 12.06 −0.26 13.0 158 3707 11.88−0.18 14.0 158 3170 11.75 −0.13 15.0 158 3036 11.65 −0.10 16.0 158 314111.56 −0.09 17.0 158 3045 11.5 −0.06 18.0 158 3062 11.43 −0.07 19.0 1583174 11.36 −0.07 20.0 158 3069 11.31 −0.05 21.0 158 3118 11.26 −0.0522.0 158 3017 11.22 −0.04 23.0 158 3140 11.17 −0.05

TABLE 2 Ultrasonic Cement Analysis of HIPE Cement with Borax Rate ofChange in Elapsed Pressure Transit Time Transit Time Time (hrs) Temp (°F.) (psi) μsec/in. μsec/in/hr. 0.0 78 3096 17.48 — 1.0 159 3279 17.9+0.5 2.0 158 3075 16.32 −1.58 3.0 158 3067 15.88 −0.44 4.0 158 315615.72 −0.16 5.0 158 3030 15.66 −0.06 6.0 158 3191 15.59 −0.07 7.0 1583128 15.57 −0.02 8.0 158 3078 15.55 −0.02 9.0 158 3035 15.52 −0.03 10.0158 3117 15.46 −0.06 11.0 158 3208 15.23 −0.23 12.0 158 3187 13.9 −1.3313.0 158 3055 12.40 −1.50 14.0 158 3300 11.78 −0.62 15.0 158 3119 11.41−0.37 16.0 158 3214 11.17 −0.24 17.0 158 3147 11.01 −0.16 18.0 158 326110.88 −0.13 19.0 158 3123 10.79 −0.09 20.0 158 3015 10.72 −0.07 21.0 1583104 10.65 −0.07 22.0 158 3019 10.6 −0.05 23.0 158 3144 10.56 −0.04

TABLE 3 Ultrasonic Cement Analysis of Neat Class A Cement Rate of Changein Elapsed Pressure Transit Time Transit Time Time (hrs) Temp (° F.)(psi) μsec/in. μsec/in/hr. 0.0 100 2787 13.08 — 1.0 160 3284 13.34 +0.262.0 159 3500 12.84 −0.50 3.0 158 3034 9.87 −2.97 4.0 158 3026 9.15 −0.725.0 158 3087 8.8 −0.35 6.0 158 3130 8.59 −0.21 7.0 158 3038 8.44 −0.158.0 158 2995 8.33 −0.11 9.0 158 2999 8.23 −0.10 10.0 158 3019 8.13 −0.1011.0 158 3042 8.05 −0.08 12.0 158 2995 7.99 −0.06 13.0 158 3119 7.93−0.06 14.0 158 3001 7.88 −0.05 15.0 158 3039 7.84 −0.04 16.0 158 30507.8 −0.04 17.0 158 3056 7.77 −0.03 18.0 158 3109 7.73 −0.04 19.0 1583035 7.71 −0.02 20.0 158 3108 7.68 −0.03 21.0 158 3045 7.66 −0.02 22.0158 3155 7.64 −0.02 23.0 158 3085 7.62 −0.0

TABLE 4 Ultrasonic Cement Analysis of Neat Class A Cement with BoraxRate of Change in Elapsed Pressure Transit Time Transit Time Time (hrs)Temp (° F.) (psi) μsec/in. μsec/in/hr. 0.0 76 27 32.08 — 1.0 158 323913.41 −18.67 2.0 158 3196 13.41 0 3.0 158 3034 13.41 0 4.0 158 3184 13.4−0.01 5.0 158 3061 13.4 0 6.0 158 3120 13.39 −0.01 7.0 158 3060 13.2−0.19 8.0 158 2995 12 −1.2 9.0 158 2999 10.29 −1.71 10.0 158 3064 9.43−0/86 11.0 158 3158 8.97 −0.46 12.0 158 3000 8.71 −0.26 13.0 158 30238.54 −0.17 14.0 158 3182 8.41 −0.13 15.0 158 3002 8.32 −0.09 16.0 1583019 8.25 −0.07 17.0 158 3023 8.18 −0.07 18.0 158 2999 8.13 −0.05 19.0158 3047 8.08 −0.05 20.0 158 3086 8.04 −0.04 21.0 158 2999 8.01 −0.0322.0 158 3165 7.98 −0.03 23.0 158 3083 7.95 −0.03

Another test comparison involved cement crush testing of 4 samples. Thefirst sample included HIPE cement. The second sample included HIPEcement with the addition of a set retarder (Borax). The third sampleincluded neat cement and the fourth sample included neat cement with theaddition of a set retarder (Borax). The results of these tests areindicated in FIGS. 3 and 4. The results are also indicated in the tablesbelow as follows:

TABLE 5 Crush Analysis of HIPE Cement Time (sec) Position (in.) Force(lb_(f)) Stress (psi) 0 0.0035 0.8303 0.2643 0.5 0.0042 6.941 2.2091.016 0.0069 98.97 31.5 1.516 0.0094 444.6 141.53 2.02 0.0119 1099.7350.1 2.5 0.0143 1905.4 606.5 3 0.0168 2888 919.2 3.5 0.0193 3962 1261.14 0.0218 5103 1624.4 4.52 0.0243 6365 2026 5 0.0267 7442 2369 5.5 0.02928556 2723 6 0.0318 9645 3070 6.5 0.0342 10670 3396 7 0.0367 11439 36417.5 0.0392 12211 3887 8.02 0.0419 12772 4066 8.5 0.0443 12865 4095 8.750.0456 12685 4038 9 0.0468 11936 3799 9.5 0.0493 6499 2069 10 0.05186369 2027

TABLE 6 Crush Analysis of HIPE Cement with Borax Time (sec) Position(in.) Force (lb_(f)) Stress (psi) 0 0.0001 2.937 0.935 1.031 0.00015.518 1.756 2.03 0.0005 36.03 11.469 3.02 0.0015 184.75 58.808 4.030.0027 465.7 148.237 5.03 0.0038 848 269.927 6.03 0.005 1284.9 408.996 70.0061 1752.9 557.965 8.03 0.0073 2266 721.29 9.03 0.0085 2797 890.31310 0.0096 3331 1060.29 11.03 0.0108 3906 1243.318 12.03 0.0119 44821426.665 13.03 0.0131 5064 1611.921 14 0.0142 5634 1793.358 15.03 0.01546217 1978.933 16.03 0.0166 6780 2158.141 17.03 0.0177 7333 2334.16618.02 0.0188 7868 2504.462 19.03 0.02 8409 2676.668 20 0.0212 89122836.778 21 0.0223 9370 2982.564 22 0.0235 9823 3126.758 23 0.0246 102543263.95 24 0.0258 10665 3394.775 25 0.0269 11026 3509.685 26 0.028111373 3620.138 27 0.0293 11687 3720.088 28 0.0304 11967 3809.214 290.0316 12222 3890.383 30 0.0328 12452 3963.595 31 0.0339 12646 4025.34732 0.0351 12778 4067.364 33 0.0363 12868 4096.012 34 0.0375 129264114.474 35 0.0386 12653 4027.575 36 0.0398 12462 3966.778 37 0.041310347 3293.552 38 0.0422 9780 3113.071 39 0.0433 9795 3117.845 40 0.04459809 3122.302

TABLE 7 Crush Analysis of Neat Cement Time (sec) Position (in.) Force(lb_(f)) Stress (psi) 0 0 — — 1.012 — — — 2.01 0.0003 65.57 20.872 30.0014 308.8 98.294 4.01 0.0026 713.2 227.019 5.01 0.0037 1213.3 386.2056.01 0.0049 1760.6 560.416 7.02 0.006 2301 746.118 8.02 0.0072 2966944.107 9.02 0.0083 3636 1157.375 10 0.0095 4346 1383.375 11.02 0.01075079 1616.696 12.02 0.0118 5858 1864.659 13.02 0.013 6667 2122.172 14.020.0141 7550 2403.24 15.02 0.0152 8487 2701.496 16.02 0.0164 95123027.764 17 0.0176 10541 3355.305 18.02 0.0187 11583 3686.983 19.020.0199 12644 4024.71 20 0.0211 13630 4338.564 21 0.0222 14534 4626.31622 0.0235 15118 4812.209 23 0.0244 15887 5056.989 24 0.0257 168125351.426 25 0.0268 17387 5534.454 26 0.028 17616 5607.347 27 0.029617058 5429.73 28 0.0305 12768 4064.181 29 0.0316 12797 4073.412

TABLE 8 Crush Analysis of Neat Cement with Borax Time (sec) Position(in.) Force (lb_(f)) Stress (psi) 0 0.0001 — — 1.031 0.0036 190.05 60.492.03 0.0085 2465 784.5 3.02 0.0135 6147 1956.5 4.02 0.0183 10552 33595.02 0.0234 15275 4862 6.02 0.0284 18568 5910 7.02 0.0342 12552 39958.03 0.0388 3275 1042.4 9.03 0.0436 2971 945.6

The term “cementitious composition” as may be used herein includespastes (or slurries), mortars, and grouts, such as oil well cementinggrouts, shotcrete, and cement compositions including a hydraulic cementbinder. The terms “paste”, “mortar” and “concrete” are terms of art:pastes are mixtures composed of a hydratable (or hydraulic) cementbinder (usually, but not exclusively, Portland cement, Masonry cement,Mortar cement, and/or gypsum, and may also include limestone, hydratedlime, fly ash, granulated blast furnace slag, and silica fume or othermaterials commonly included in such cements) and water; “mortars” arepastes additionally including fine aggregate (e.g., sand), and“concretes” are mortars additionally including coarse aggregate (e.g.,crushed rock or gravel). The cement compositions described in thisinvention are formed by mixing required amounts of certain materials,e.g., a hydraulic cement, water, and fine and/or coarse aggregate, asmay be required for making a particular cementitious composition.

The term “accelerator” can include any component, which reduces thesetting time of a cement composition. For example, the accelerator mayinclude alkali and alkaline earth metal salts, such as a calcium salt.The calcium salt may include calcium formate, calcium nitrate, calciumnitrite or calcium chloride.

The term “oxidizer” can include any component which is capable ofdegrading the retarder present. These include, but are not limited toalkaline earth and zinc salts of peroxide, perphosphate, perborate,percarbonate; calcium peroxide, calcium perphosphate, calcium perborate,magnesium peroxide, magnesium perphosphate, zinc perphosphate, calciumhypochlorite, sodium persulfate, organic peroxides, organichydroperoxides, magnesium hypochlorite; and mixtures thereof.

The term “retarder” or “set retarder” can include boronated ornon-boronated forms of phosphonic acid, phosphonic acid derivatives,lignosulfonates, salts, sugars, carbohydrate compounds, organic acids,carboxymethylated hydroxyethylated celluloses, synthetic co- orter-polymers including sulfonate and carboxylic acid groups, and/orborate compounds.

The term “set” as used herein refers to an increase in mechanicalstrength of a fluid or slurry sufficient to perform a desired result,such as to restrict movement of an item or impede fluid flow or pressuretransfer through a fluid. A cement may be referred to as set when it canrestrict the movement of a pipe, or impede fluid flow or pressuretransfer, regardless of whether the cement has cured to a fully solidcomposition. A fluid or slurry can be referred to as set when it hasthickened to a sufficient level that it achieves the desired result,such as the isolation of a particular zone or the restriction of fluidflow or pressure transfer, regardless of whether it has reached itsfinal consistency.

Depending on the context, all references herein to the “invention” mayin some cases refer to certain specific embodiments only. In other casesit may refer to subject matter recited in one or more, but notnecessarily all, of the claims. While the foregoing is directed toembodiments, versions and examples of the present invention, which areincluded to enable a person of ordinary skill in the art to make and usethe inventions when the information in this patent is combined withavailable information and technology, the inventions are not limited toonly these particular embodiments, versions and examples. Other andfurther embodiments, versions and examples of the invention may bedevised without departing from the basic scope thereof and the scopethereof is determined by the claims that follow.

While compositions and methods are described in terms of “comprising,”“containing,” or “including” various components or steps, thecompositions and methods can also “consist essentially of” or “consistof” the various components and steps. All numbers and ranges disclosedabove may vary by some amount. Whenever a numerical range with a lowerlimit and an upper limit is disclosed, any number and any included rangefalling within the range is specifically disclosed. In particular, everyrange of values (of the form, “from about a to about b,” or,equivalently, “from approximately a to b,” or, equivalently, “fromapproximately a-b”) disclosed herein is to be understood to set forthevery number and range encompassed within the broader range of values.Also, the terms in the claims have their plain, ordinary meaning unlessotherwise explicitly and clearly defined by the patentee.

The invention claimed is:
 1. A method comprising: placing a sealantcomposition into a subterranean formation after drilling of a wellboretherein; wherein the sealant composition comprises an emulsion of aninternal aqueous phase and an external organic phase, and wherein theinternal aqueous phase comprises cement slurry, the cement slurrypresent in the aqueous phase in an amount of about 75% to about 95% byvolume of the aqueous phase; subjecting the sealant composition to athermal source; wherein subjecting the sealant composition to thethermal source alters the external phase and the internal phase.
 2. Themethod of claim 1, wherein the organic phase comprises a crosslinkingagent.
 3. The method of claim 1, wherein the internal phase and externalphase are immiscible with each other.
 4. The method of claim 1, whereinthe thermal source is naturally occurring within the wellbore.
 5. Themethod of claim 1, wherein the thermal source emits thermal energy thatis induced by technicians in the field.
 6. The method of claim 1,further comprising locating a thermal emitter into the wellbore andreleasing thermal energy from the emitter.
 7. The method of claim 1,wherein the internal phase is present in the emulsion in amounts of fromabout 50% to about 90% of the total volume of the emulsion.
 8. Themethod of claim 1, wherein the external phase is present in the emulsionin amounts of from about 10% to about 50% of the total volume of theemulsion.
 9. The method of claim 1, wherein the emulsion has avolumetric ratio of internal phase to external phase of from 9:1 to 1:1.10. The method of claim 1, wherein subjecting the sealant composition tothe thermal source alters the external phase resulting in an increase inthe mechanical strength of the sealant composition.
 11. The method ofclaim 1, wherein the organic phase comprises a thermo-setting resin. 12.The method of claim 11, wherein subjecting the sealant composition to athermal source initiates the setting of the thermo-setting resin. 13.The method of claim 1, wherein the aqueous phase further comprises a setmodifier.
 14. The method of claim 13, wherein the set modifier isselected from the group consisting of an accelerator, an oxidizingagent, a set retarder, and combinations thereof.
 15. The method of claim1, wherein the sealant composition further comprises an initiator. 16.The method of claim 15, wherein the initiator is selected to initiatethe altering of the external phase at a temperature of at least aportion of the wellbore.
 17. The method of claim 15, wherein theinitiator is selected from the group consisting of azo-initiators. 18.The method of claim 15, wherein the initiator is selected from the groupconsisting of peroxy-initiators.
 19. The method of claim 15, wherein theinitiator is selected from the group consisting of2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile),2,2′-azobis(2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile,dimethyl 2,2′-azobisisobutyrate, 2,2′-azobis(2-methylbutyronitrile),1,1′-azobis(1-cyclohexanecarbonitrile),2-(carbamoylazo)isobutyronitrile, 2,2′-azobis(2,4,4-trimethylpentane),2-phenylazo-2,4-dimethyl-4-methoxyvaleronitrile,2,2′-azobis(2-methylpropane), persulfates, benzoyl peroxide, tert-butylperoxide, and combinations thereof.
 20. The method of claim 15, whereinthe initiator initiates the altering of the external phase.
 21. Themethod of claim 20, wherein the initiator initiates the altering of theexternal phase upon reaching a temperature threshold.
 22. The method ofclaim 1, wherein the organic phase comprises a monomer.
 23. The methodof claim 22, wherein the monomer is selected from the group consistingof methyl acrylate, ethyl acrylate, butyl acrylate, methylstyrene,styrene and methyl methacrylate and combinations thereof.
 24. The methodof claim 22, wherein the monomer is polymerized to form a polymericcomponent.
 25. The method of claim 24, wherein subjecting the sealantcomposition to a thermal source initiates the polymerization of themonomer.
 26. The method of claim 24, wherein the aqueous phase setswithin the structure of the polymeric component.
 27. The method of claim24, wherein an initiator initiates the polymerization of the monomer toform a polymeric component.
 28. A method comprising: placing a sealantcomposition into a subterranean formation after the drilling of awellbore therein, the sealant composition comprising an emulsion of aninternal phase and an external phase that are immiscible with eachother; and subjecting the sealant composition to a thermal source;wherein the internal phase comprises an aqueous phase that comprisescement slurry and the external phase comprises an organic phase thatcomprises at least one of a monomer or a thermo-setting resin; whereinthe cement slurry is present in the aqueous phase in an amount of about75% to about 95% by volume of the aqueous phase; and wherein subjectingthe sealant composition to the thermal source alters the external phaseby at least one of polymerizing the monomer or setting the resin,resulting in an increase in the mechanical strength of the sealantcomposition.